The present invention relates generally to an apparatus and method for applying coating materials to a plurality of overlapped individual sheets, such as individual sheets of paper. A specific aspect of the invention relates to an apparatus and method for applying a coating material to both opposing major surfaces of a plurality of individual sheets.
It is often necessary to apply coating materials to paper and, in some cases, to apply different coating materials to both major surfaces of the paper. For example, in the production of repositionable notes, such as the Post-It(copyright) brand note pads available from Minnesota Mining and Manufacturing Company, it is known to apply a primer material to one side of the paper from which the repositionable notes will be cut, and to apply a low adhesion backsize, or release, material to the other side of the paper. Repositionable adhesive is then applied to the paper on top of the primer material. Conventionally, for the production of repositionable notes, the various coatings are applied to a web of paper drawn from a continuous roll. The coating materials are dispersed in solvents and coated directly onto the paper web. The web is dried between coatings and then rewound, with the coated roll subsequently cut into sheets which are used to produce the notes.
A process for the production of repositionable notes, in which a release material and a primer material are coated successively on opposite sides of a paper web, is described in WO-A-87/05315.
In some cases, it is desirable to apply coating material to cut sheets rather than to a continuous web of paper. For example, in the production of repositionable notes it is often desirable to have the option of using a stack of preprinted sheets as the supply source, instead of a plain paper web, to extend the flexibility of the production process. In addition, for environmental reasons, there is a desire to move away from the use of environmentally destructive organic solvents in such coating processes, and towards more environmentally friendly water-based materials. It is moreover noted that many inks are soluble in organic solvents, but insoluble in water.
WO 94/19419 discloses an apparatus and a method for forming pads of repositionable notes from a stack of uncoated individual paper sheets. The sheets are fed from the stack in an overlapped condition to a coating station in which a continuous layer of a water-based primer material is applied to one major surface of the pseudo web of overlapped sheets, and a continuous layer of a water-based low adhesion backsize (LAB) material is applied simultaneously to the other major surface. The overlapped sheets are then dried and fed to a second coating station in which stripes of repositionable adhesive are transferred from an endless transfer belt to the pseudo web of overlapped sheets onto the surface to which the primer was applied in the first coating station. Thereafter, the sheets are adhered together in a stack and trimmed to form pads of repositionable notes.
Coating of Individual Sheets
In certain coating processes, it may be preferable for sheets to be coated individually rather than in the form of an overlapped pseudo web. However, commercial coating stations are generally designed for coating a continues web of paper dispensed from a large roll, and cannot accommodate individual sheets.
Hence, efforts continue to develop a commercially viable system that will enable the coating of individual sheets with an effective amount of coating material.
Reversing Direction of Overlap
In certain circumstances, the handling of overlapped individual sheets can be facilitated by reversing the direction of the overlap as the sheets pass through certain segments of the coating process. When such a reversal in the direction of overlap is desired, the apparatus used to achieve the reversal should function reliably for a wide range of sheet sizes, weights and types.
It has been found that existing systems for applying a coating material to sheets, while having their own utility, are not as effective and flexible as desired. It has also been found that existing systems which use an endless transfer surface for applying a coating material to sheets commonly encounter problems in removing the sheets and the coating material from the transfer surface when certain types of coating materials and/or certain types and sizes of sheets are being coated. Therefore, an improved method and apparatus for applying coating materials onto sheets, including an improved method and apparatus for transferring a coating material from an endless transfer surface to sheets, is desired.
Inserting Secondary Sheets
The sheet inserter aspect of the present invention provides an apparatus and a method effective for periodically inserting a different secondary sheet into a sequence of overlapped sheets which are to be coated. The apparatus includes (i) a sheet feeder operable to sequentially feed primary sheets from a stack of primary sheets onto a conveyor in end-to-end overlapping relationship to each other, (ii) a sheet inserter operable to insert at least one secondary sheet, from a second stack, into the overlapped primary sheets on the conveyor, and (iii) a coater positioned to receive the overlapped sequence of primary and secondary sheets from the conveyor and operable to apply coating material to at least one major surface of each sheet.
The method comprises the ordered steps of: (a) feeding primary sheets from a first sheet stack onto a sheet path in end-to-end overlapping relationship to each other, (b) conveying the overlapped primary sheets along the sheet path, (c) inserting at least one secondary sheet, from a second sheet stack, into the overlapped primary sheets being conveyed along the sheet path, so as to form a sequence of primary and secondary sheets arranged in end-to-end overlapping relationship to each other, and then (d) applying a coating material to at least one major surface of each of the primary and secondary sheets in the sequence as the sheets continue to be conveyed along the sheet path.
Dual Coating of Individual Sheet Members
The dual coating aspect of the present invention provides an apparatus and a method for simultaneously applying a water-based coating material to both major surfaces of separated individual sheet members. The apparatus includes (i) a dual coating system positioned to sequentially receive single sheet members as the sheet members are conveyed along a sheet path, the coating system comprising first and second coating mechanisms located on opposed sides of the sheet path with each coating mechanism operable to apply a water-based coating material to a major surface of each sheet; (ii) a dryer positioned along the sheet path for removing water from the water-based coating materials applied to the sheets by the coating mechanism, (iii) means for arranging sheets as they exit from the drier in sequential end-to-end overlapping relation, and (iv) a secondary coating mechanism positioned along the sheet path which is effective for receiving the overlapped sheets and applying a secondary coating material to one side of the overlapped sheets.
The method comprises the ordered steps of: (a) sequentially feeding individual sheets from a first sheet stack onto a sheet path, (b) conveying the overlapped primary sheets along the sheet path, (c) applying a water-based coating material to a major surface of each individual sheet being conveyed along the sheet path, (d) drying the coated sheets while continuing to convey the sheets along the sheet path; (e) arranging the dried sheets in sequential end-to-end overlapping relationship to each other, and then (f) continuously applying a second coating material to at least one major surface of each of the arranged sheets as the sheets continue to be conveyed along the sheet path.
Padded Coating Drum
The covered coating drum aspect of the present invention provides an apparatus and a method for applying a coating material to at least one major surface of separated individual sheet members. The apparatus includes (i) a coating roller; (ii) a support sheet releasably secured over the surface of the coating roller, (iii) an elastomeric covering member adhesively secured to the support sheet which extends over only a portion of the circumference of the coating roller, (iv) a nip roller which cooperates with the coating roller to form a nip only with that portion of the coating roller which is covered with the covering member; (v) a source of coating material, and (vi) a means for applying coating material from the source of coating material to the covering member on the coating roller.
The method comprises the ordered steps of: (a) applying coating material from the source of coating material to the covering member on the coating roller, and (b) conveying individual sheets into the nip formed between the coating roller and the nip roller in such a manner that the sheet is registered and aligned with the covering member on the coating roller such that the coating material on the covering member is transferred to the sheet without being transferred to the nip roller.
Reversing Direction of Overlap
The overlap altering aspect of the present invention provides an apparatus and a method for reversing the direction in which the sheets are overlapped. The apparatus includes (a) a first conveyor means for transporting a succession of overlapped sheets wherein the trailing edge of each sheet is positioned underneath the leading edge of the succeeding sheet; (b) a second conveyor means arranged to receive sheets from the first conveyor means; and (c) an arrangement, positioned between the first and second conveyor means, effective for changing the relative overlapping positions of the sheets; whereby the sheets received by the second conveyor means are arranged with the trailing edge of each sheet positioned over the leading edge of the succeeding sheet. The arrangement effective for changing the relative overlapping positions of the sheets comprises (A) a blower for directing a current of air at the overlapped edges of each pair of sheets so as to move such edge portions away from the plane defined by the succession of sheets, and (B) a means for retarding the subsequent return of the trailing edge of the leading sheet so as to ensure that such trailing edge will consistently be deposited on top of the leading edge of the succeeding sheet.
A preferred embodiment of the overlap altering aspect of the invention positions the overlap altering arrangement between the dual coating system and the dryer of the dual coat aspect of the invention. In this embodiment, the sheets are coated one at a time in the dual coating system and then deposited on a first conveying means with the trailing edge of each sheet positioned underneath the leading edge portion of the succeeding sheet. As the overlapped sheets are transferred from the first conveying means to a second conveying means for transportation into the dryer, the overlap altering arrangement reverses the relative overlapping positions of the sheets whereby the trailing edge of each sheet is positioned on top of the leading edge portion of the succeeding sheet.
The method comprises the ordered steps of: (i) conveying a succession of overlapped sheets on a first conveying means, wherein the trailing edge of each sheet is positioned underneath the leading edge of the succeeding sheet; (ii) transferring the overlapped succession of sheets from the first conveyor means to a second conveyor means; and (iii) changing the relative overlapping positions of the sheets as the sheets are transferred from the first conveying means to the second conveying means so that the sheets received by the second conveyor means are arranged with the trailing edge of each sheet positioned over the leading edge of the succeeding sheet. The preferred means by which the relative overlapping positions of the sheets is changed includes the steps of (I) blowing a current of air at the overlapped edges of each pair of sheets so as to move such edge portions away from the plane defined by the succession of sheets, and then (II) retarding the subsequent return of the trailing edge of the leading sheet so as to ensure that such trailing edge will consistently be deposited on top of the leading edge of the succeeding sheet.
Detachment of Coated Sheets From a Transfer Surface
The sheet detachment aspect of the present invention provides an apparatus and a method for facilitating the consistent removal of overlapped sheets and coating material from a transfer surface used to transport coating material into contact with a pseudo-web of overlapped sheets. The sheet detachment apparatus is particularly useful in connection with a transfer system designed to transfer an at least partially dried coating material to a pseudo-web of overlapped sheets. Briefly, such a transfer system conveys a pseudo-web of overlapped sheets to a transfer location where an endless transfer surface, moving in the same direction and at the same speed as the pseudo-web, contacts a major surface of the conveyed sheets for purposes of transferring a coating material from the transfer surface to the sheets in the pseudo-web. The coating material is remotely applied to the transfer surface by a dispensing device which is capable of applying various types of coating materials at various thickness and variable patterns to the transfer surface.
The sheet detachment apparatus includes (a) a detachment conveyor located adjacent the path of the sheets leaving the transfer location; and (b) a source of reduced pressure operable for (A) providing an area of reduced pressure over a first length of the detachment conveyor, positioned closest to the transfer location, effective for detaching sheets from the transfer surface and attracting the sheets to the detachment conveyor and, (B) providing an area of reduced pressure over a second length of the detachment conveyor effective for keeping the sheets attached to the detachment conveyor as the sheets are moved away from the transfer location.
The method comprises the ordered steps of: (i) conveying a pseudo-web of overlapped sheets along a sheet path and through a transfer location, (ii) applying a coating material to the surface of an endless transfer surface, (iii) contacting a first major surface of the sheets in the pseudo web with the coated endless transfer surface as the sheets are conveyed through the transfer location, (iv) applying a partial vacuum to that portion of the conveyor positioned immediately downstream from the transfer location effective for detaching the sheets and coating material from the transfer surface and attracting the coated sheets to the conveyor, and (v) applying a partial vacuum to the balance of the conveyor positioned downstream from the transfer location effective for keeping the coated sheets attached to the conveyor as the sheets are moved away from the transfer location.